In wireless communication, it may be necessary to transmit more than one DCI. For example, for NAICS (Network-Assisted Interference Cancellation and Suppression), a new DCI is needed to indicate interference. NAICS is SI (Study Item) in LTE (Long Term Evolution) Rel.12 and targeted to realize advanced receiver to cancel/suppress interference in UE side by assistance of network signaling. The main task of NAICS SI is to investigate an enhanced receiver with network-assistant for mitigating the co-channel interference coming from inter-cell, intra-cell, or inter-stream.
In NAICS, with the help of eNB indication, an advanced receiver at UE could estimate the effective channel of the interference signal, demodulate the interference signal, and decode the interference signal. For purpose of cancelling/suppressing interfering signals, the advanced receiver at UE should obtain the necessary information about interfering signals through indication from network for channel estimation/demodulation/decoding.
As interference could be a dynamically scheduled signal of interfering cell, such interference indication could be a unicast indication of L1 signaling (e.g., Physical Downlink Control Channel (PDCCH) or enhanced PDCCH (EPDCCH)) from serving cell if backhaul is ideal, while some long-term information, such as cell-specific information, can be signaled by Radio Resource Control (RRC). Some interference parameters, which probably need a certain degree of scheduling restriction in serving/neighbor cell or more decoding complexity in victim UE, can also be blind detected by victim UE. For example, PhysCellID (PCI) of neighbor cell can also be detected by cell search procedure instead of RRC signaling, RB (Resource Block) allocation of DMRS (Demodulation Reference Signal)-based transmission mode (TM) interference can also be detected by checking correlation of DMRS with very restricted number instead of by L1 signaling, and modulation order can also be blind tried by receiver instead of explicit indication.
Blind detection/try will either require more processing complexity on victim UE or reduce the system performance by limiting the flexibility of scheduling. Therefore, for NAICS system design, it needs to strike a balance between UE complexity and system performance (signaling overhead and/or scheduling flexibility). Moreover, some parameters cannot be blind detected/tried in an acceptable performance loss or complexity, e.g., TPMI (Transmitted Precoding Matrix Indicator) and RB allocation of CRS (Cell-Specific Reference Signal)-based TM, and L1 signaling for such information is more proper. It is noted that, in this disclosure, the information to be transmitted in L1 signaling is not limited to the above, but any information which can be indicated through L1 signaling is included.
As BD (blind decoding) is used for L1 signaling, the BD procedure can be introduced below by using PDCCH as an example.)                Search space: number of candidates per aggregation level (AL)                    UE-specific search space (USS): total is 16 (6/AL1, 6/AL2, 2/AL4, 2/AL8)            Common search space (CSS): total is 6 (4/AL4, 2/AL8))                        Number of DCI formats monitored:                    USS: 2 [3, if DCI format 4 is supported]            CSS: 2                        Total BD trials: number of candidates×number of DCI formats monitored:                    USS: 32 [48, if DCI format 4 is supported]; CSS: 12.                        
When a second DCI (e.g., a new DCI for interference indication) is transmitted in for example USS together with a first DCI (e.g., a traditional DCI for allocating resource to UE), the total BD trials will be increased. For example, if a new DCI for interference indication is transmitted with a traditional DCI, the DCI format number in USS could be increased from 2 to 3 (from 3 to 4, if DCI format 4 is supported). The total BD trials in USS are increased by 50% (33%, if DCI format 4 is supported), and thus the increased number of BD trials is at most 16. The problem of the traditional way is that BD receiver would need 150% (133%, if DCI format 4 is supported) of decoding capability to keep the decoding delay unchanged (which is a large modification in UE chipset) or BD receiver would result in 150% (133%, if DCI format 4 is supported) of decoding delay if the decoding capability remains the same (resulting in less time left for PDSCH decoding especially for EPDCCH indication). Therefore, how to reduce the additional BD trials introduced by the second DCI is very important for realistic implementation.